This invention relates to a magnetic playback apparatus for playing back, by a magnetic head, a signal recorded on a rotating magnetic recording medium (e.g., a video floppy) and, more particularly, to methods of detecting and deciding the peak position of an envelope of a recorded signal necessary for positioning the magnetic head at the center of a recorded track in order to achieve excellent recorded signal playback.
The magnetic playback apparatus mentioned here is a concept which includes a magnetic recording apparatus having a playback function (e.g., a still-video camera), a magnetic playback apparatus having a recording function, and a magnetic recording/playback apparatus.
Recording of a still-video signal on a video floppy (a magnetic recording medium) in a still-video camera is carried out by positioning a magnetic head on an absolute track position in accordance with an absolute track address system. On the other hand, a video floppy undergoes expansion and contraction due to environmental changes, especially changes in temperature and humidity. As a result, some deviation or offset occurs between the center of a recorded track on a video floppy and the absolute track position.
In playing back a still-video signal, it is desired that the best signal having little noise be read from the video floppy. In order to achieve this, it is necessary that the center of the magnetic head be made to coincide with the center of the portion of the video floppy on which the signal is actually recorded. At a recorded track on a video floppy, it is required to execute processing for detecting the peak position of the envelope of the read signal obtained when the magnetic head is fed in the diametric direction (i.e., across the track). This is peak position detection processing and is performed by comparing detected envelope levels at neighboring envelope detection positions and moving the magnetic head in the direction of the higher envelope level.
Conventionally, feed of the magnetic head and measurement of the detected envelope value are repeated until the peak position is decided. In actuality, since a change occurs in the envelope level detected even at the same position, it is not easy to decide where the peak position is located and therefore peak position detection processing requires a comparatively long period of time.
In the aforementioned peak position detection processing, peak position cannot be detected when no envelope is detected at all or when the envelope does not attain a prescribed level.
Though it can be considered that a signal has not been recorded on a track when no envelope is detected at that track, there is a case in which it can be surmised that a signal should be recorded on the track despite the absence of the envelope.
Specifically, consider a case in which the apparatus is a still-video camera having a playback function. In a still-video camera, an imaged video signal can only be recorded on a blank track of the video floppy. In order to readily determine whether each track has been recorded on or whether each track is blank, a track search is performed within the camera when a video floppy is loaded or when one video floppy is exchanged for another, and the results of the track search are preserved in the form of a track map.
If a designated track is a recorded track, an operation for playing back this track is performed in the playback mode. The abovementioned peak position detection processing is performed at the beginning of this playback operation. Despite the fact that the track is determined to be a recorded track in the track search processing, there are occasions where an envelope can fail to be detected at the same track in peak position detection processing because of poor contact between the magnetic head and the magnetic disk, or for some other reason. In any event, even in this case the position of the center of the track must be decided in order to make the transition to the playback operation.